posted 02-06-2013 01:32 PM ET (US)        

As I understand it--and this could very likely be wrong--the present regulations of the EPA and CARB require outboard engines to meet a standard of exhaust gas emission. The standard imposes a limit on the amount of controlled exhaust gas emitted based on the operation of the engine as measured by power output and time. (I will just call these controlled exhaust gases "air poilution" as a general name.) For example, a certain exhaust gas emission of a particular combustion product is regulated by allowing only so much volume or weight of the exhaust gas per unit of power and time. If this is not correct, I would like someone to reply and give me a more precise explanation. But let me proceed with the assumption that I have correctly stated the regulating process. For example, if you run a particular engine at 100-HP for one hour, you are allowed to produce a certain amount of a certain exhaust gas and no more; if you make too much you do not meet the standard.

I do not see where fuel economy plays a role in these ratings. I do not see any regulations that would restrict the amount of fuel burned to produce the horsepower. This sort or regulation appears to be different from the regulations imposed on automobiles. Automobiles have to meet emission standards and fuel economy standards simultaneously. Apparently outboard engines only have to meet emission standards.

I have two insights to offer. First, it would be impossible to measure fuel economy of outboard engines in terms of miles-per-gallon because the hull design of the boat they were used with, along with the propeller, have a very significant influence. So it seems reasonable that CARB and EPA regulations make no mention of fuel economy in terms of miles-per-gallon.

Next, it seems that fuel economy is actually part of the emission standard already, in an indirect manner. Because the emission standard is imposed on a basis of exhaust output per unit of horsepower-hour, it seems that the less fuel burned to produce the power the less exhaust gas emission being produced. For example, if engine-A burns 10-gallons of gasoline in one hour making 100-HP, and if engine-B burns 11-gallons of gasoline in one hour making 100-HP, it seems very clear that the engine using less gasoline will have an advantage in meeting the emission standard. The less fuel you burn, the less exhaust gas emission (in total) there will be.

On the basis of this analysis it seems at the most fundamental level, good fuel economy in an outboard motor naturally tends to produce lower exhaust gas emission, and lower exhaust gas emission means it should be easier to meet the regulations for exhaust gas emission by weight per horsepower-hour.

In fact, we see this trend. All of the engines meeting the emission standard get significantly better fuel economy than engines that do not. I can testify to this first hand. My old carburetor high-emission engine got 1.8-MPG at displacement speed. My new direct-injection ultra-low-emission engine gets three or four times better fuel economy at that same boat speed, about 7-MPG.

We all know that if a certain amount of fuel is burned, there is going to be a corresponding amount of exhaust gas created from the combustion. In the exhaust gas there are good components and bad components. The usual products of all combustion of hydrocarbon fuels are water and carbon-dioxide. In perfect combustion, the exhaust gas contains just those two compounds. In not-so-perfect combustion, the exhaust gas contains other compounds. These other compounds are the combustion products that are regulated.

The regulated exhaust gas emission are in two groups: hydrocarbons (or sometimes called reactive organic gases) and oxides of nitrogen. These compounds are measured and regulated by CARB and EPA.

I am no scientist of the combustion process, but apparently the amount of the controlled gases can vary significantly based on the many factors that occur in the combustion process. But there is still one fundamental and basic relationship: the less fuel you burn, the less exhaust gas you produce. Therefore it would seem that on a fundamental level, the EPA and CARB regulations would tend to improve fuel economy.

The fuel being burned by all engines is the same fuel. In fact, I think for the testing a very particular fuel must be used; you can't just go down to the local gasoline station and get the fuel. It has to be a specific fuel. What happens in the combustion chamber is the same for everyone; a chemical reaction takes place, and it is going to be the same reaction, based on the laws of Chemistry. Everything is equal for all engines.

Even though the fuel is the same and the laws of Chemistry are the same, not all engine combustion chambers are the same. There can be all sorts of changes. The ratio of fuel and air can be different. The temperature can be different. The pressure in the cylinder can be different. But one thing remains constant: if you use less fuel to make a certain amount of power, you will be making less exhaust gas. The engine that burns less fuel has an advantage in meeting the emission limits.

At first glance, it seems completely paradoxical that there could be a situation where an engine that burned less fuel could produce more air pollution. Or, conversely, that an engine burning more fuel to make a certain horsepower could produce less air pollution.

I also have to observe that among many manufacturers of outboard engines, all the manufacturers are able to produce engines that meet the present day highest standards of CARB and EPA with their engines, with one notable exception. The outboard engine industry as a whole has been able to produce outboard engines, across a very wide range of power levels, and using a wide range of methods and technologies, that meet the most stringent emission ratings, that is, the CARB Three-Star and the EPA 2010 ratings, and, at the same time, these engines are getting excellent fuel economy. Indeed, some of the Three-Star engines, for example the new Honda BF250, are demonstrating fuel economy that has never been seen before in an outboard engine. On that basis it seems clear that there is no inherent physical or chemical law that would exclude an outboard engine from reaching the most stringent emission requirements while producing the best fuel economy. It clearly can be done and it clearly is being done.

From this I conclude:

--improved fuel economy is beneficial to meeting emission limits

--fuel economy and emission limits are not mutually exclusive

posted 02-06-2013 02:08 PM ET (US)            

However, the carburetor mixture adjustments, unlike in older engines, are sealed and are theoretically not adjustable. Well why is this? Because if you richen the mixture by adjusting the screws, you produce more emissions and the 3-start rating would be lost BUT the engine is not running optimally at its sealed lean setting. If you remove the plugs (as I have) and richen the mixture a little, the performance of the engine is noticeably better - so I would guess that it may at a given power setting be using less gas, but the gas that it is using is producing more pollutants.

posted 02-06-2013 02:08 PM ET (US)            

quote:

---

From this I conclude:

--improved fuel economy is beneficial to meeting emission limits

--fuel economy and emission limits are not mutually exclusive

---

Jim, not 100% true. You are partially correct. It depends on which emissions compound you are talking about. The two of greatest import are unburned hydrocarbons, HC, and oxides of nitrogen, NOx. And THOSE two ARE mutually exclusive of each other. The means of reducing one of them, increases the other... except for a very narrow band of fuel mixture that is only possible and safe at low loads, such as idling, (or steady cruise in a car)).

At higher loads, such as max power or even 4500rpm cruise in a boat, you simply MUST run the motor a little bit rich, which MUST increase HC emissions, and decrease fuel economy compared to what you would get running a stoichiometric fuel mixture. Now, how rich you run in this regime is up to the engine designer and the "safety margin" against engine destruction that he is comfortable with. If he is bold, he can run leaner at high load. That will reduce HC emissions AND increase fuel economy. In that light, your statement is correct. HOWEVER, if you run (relatively) lean at high load, you will INCREASE the production of NOx (oxides of nitrogen). In light of that, fuel economy and emissions ARE in fact, mutually exclusive.

It is this narrow apex of emissions control where decreasing HC, increases NOx, and vice versa, where catalytic converters come in. With a cat, it makes having your cake and eating it too, (emissions-wise) much more feasible. The staggering cost, weight, and complexity of adding a cat or cats to an outboard have been discussed elsewhere and I'm sure they will continue to be.

My prediction (and I hope I'm wrong): We will have cats on outboards one day. And it will be as complex, expensive, and ugly as some are predicting. But 90% of us will still be just as desperately excited to buy one as we are over four strokes today.

posted 02-06-2013 02:52 PM ET (US)            

I believe in the regulations there are weighting factors. An engine does not have to qualify at every possible combination of throttle and load conditions. There are several defined testing points. The emissions are measured at those points, and then those points are weighted. The weighted average emission over the whole range of load and operating conditions is what becomes the rating factor. (Again, if this is not correct, let me know.)

The use of multiple points of power and load, and a weighting of those (which is probably according to some model of he typical pattern of use for an outboard) provides the engine designer with the ability to run the engine somewhat differently at high-load settings than at low-load settings. The engine designer can run a rich mixture when needed and a lean mixture when more advantageous.

Further, the tolerance of an engine to resist failure in certain operating conditions is really a function of its design. The more robust the design, then the more likely the engine will operate without failing, even at certain operating conditions where it is subject to maximum stress. I recognize that adding more fuel is a useful way to relieve some of the stresses, but at the same time there must be other methods to relieve those stresses. For example, increased strength of materials, better cooling, and in general craftier design could be employed. This must be true because we have evidence. Almost every outboard engine manufacturer can make engines, even engines of over 200-HP, that simultaneously meet the most strict emission standards and give good fuel economy. Clearly those engineers have solved the problem. This means there are solutions to the problem.

It may very well be that to arrive at the solution to the problem requires using a certain path or method. If someone designs an engine using a method, a path, that just cannot lead to the solution, this is not proof that there is no path to the solution. They just took the wrong path.

I can appreciate that an engine manufacturer may be stuck on a path. If an engine manufacturer adopts a certain approach to the design of an outboard engine, spends $150-million developing that approach, and discovers, at the end of the road, their method cannot solve the problem, they may be stuck. Outboard engines are a boutique product, and you cannot get $150-million to develop new ones very easily.

posted 02-06-2013 03:02 PM ET (US)            

The leaner you run at higher loads, the more NOx emissions you will produce. Period. Even if such lean running increases fuel mileage and decreases HC emissions. Thus, tuning for good fuel economy increases one bad emissions product, while decreasing another. It suck, I know. But didn't make that rule. God did. As for the details of the regulator's rules that allow engine makers to work with that physical fact, I defer to you. But it is incorrect from the standpoint of physics, to say that tuning for better fuel economy, reduces emissions in their entirety. It only reduces one of the two big emissions, while increasing the other.

posted 02-06-2013 04:20 PM ET (US)            

From
http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=0b807b404a9925a56fc1deebfed16a6a&rgn=div5&view=text&node=40:34.0.1.1.8&idno=40

§ 1045.103 What exhaust emission standards must my outboard and personal watercraft engines meet?
(a) Duty-cycle emission standards. Starting in the 2010 model year, exhaust emissions from your outboard and personal watercraft engines may not exceed emission standards as follows:

(1) Measure emissions using the applicable steady-state test procedures described in subpart F of this part.

(2) The exhaust emission standards from the following table apply:

Table 1 to § 1045.103—Emission Standards for Outboard and Personal Watercraft Engines (g/kW-hr)

posted 02-06-2013 04:26 PM ET (US)            

Here is the data table. Note that the units for all emission standards shown is g/kW-hr, which is mass of emissions per unit of power generated.

Emission standard g/kW-hr
HC + NOX
Power > 4.3 kW (6 hp)
2.1 + 0.09 × (151 + 557/P^0.9)
CO
Power > 40 kW (54 hp)
300

[A kW is 1.341 hp. There are different standards for lower power units. There are also various averaging approaches you can read about in the rule from the above web address]

So, jimh, you understand it correctly. If an outboard is more efficient at making power, it can emit more pollution per unit of fuel input. This does incentivize efficient engines.

posted 02-06-2013 05:47 PM ET (US)            

*BSFC = Brake Specific Fuel Consumption

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

posted 02-06-2013 08:19 PM ET (US)            

We can't really tell from the EPA test data or the CARB test data which engine will burn more fuel. I understand that you are able to interpret the Mercury test data to mean the Mercury will burn less fuel. That is only what Mercury says, and you would expect them to say that. I have never seen any real data by an independent tester that shows a particular advantage. But assuming you are correct, and the E-TEC used more fuel during that hour, it would have still produced less air pollution.

posted 02-07-2013 07:57 AM ET (US)            

Larry -- I presume you are relying on your favorite Mercury head-to-head advertisement for your statement. So what about the fact that your favorite advertisment in the confusing Gallons Per Hour graph represents that the Verado 150 burns 12.1 GPH at WOT but yet there is NOT A SINGLE, I repeat NOT A SINGLE, performance for the Verado 150 (Mercury created or 3rd party created) within the Mercury performance report library available on the Mercury Marine website that backs that representation up?

FYI, one of the performance reports in the library done by a 3rd party rather than Mercury shows the Verado 150 burning 18+ GPH at WOT! Most of the other reports show consumption in the 14.5 to 15 GPH range. Either way, that's a quite a gap from the 12.1 GPH in the advertisement.

Seems to me that your favorite head-to-head advertisment has a bit of a credibility problem.

Regarding emissions, as engine makers try to lean out the mixture to maximize fuel economy, it is possible that the more fuel efficient motor might not meet the highest emissions tier because, as I understand, even if the HC component goes down, the NOx component might go up such that the total of the two exceeds the highest emission tier's limit.

posted 02-07-2013 04:37 PM ET (US)            

quote:

---

Not quite Peter. If the BSFC is better (more efficient) you can emit more pollution per heat input (e.g., more mass of pollution per gallon of fuel)

---

posted 02-08-2013 09:31 AM ET (US)            

For a 225-HP engine, the power rating in kW is 225/1.341 or 167.8-kW. Since this is above the threshold of 40kW, the engine is allowed to emit 300-g/kW-hour of CO. This means that if I run my engine at full-throttle for one hour, I can emit up to

167.8-kW x 1-hour x 300-g/kW-hour = 50340-grams or 50.340-kg

That is 111-lbs of CO.

For the HC + NOx component, I calculate a limit of 16.19-g/kW-hour. An hour at full throttle should produce no more than 5.9-lbs.

Let's say the 225-HP engine was burning 20-GPH of gasoline that weighs 6.25-lbs/gallon. The fuel burned would have weighed 125-lbs.

DId I calculate these three weights properly?

posted 02-09-2013 01:22 AM ET (US)         

quote:

---

Why does forced-induction have this effect on the emissions (or does it)?

---

Yes. It increases combustion temperatures which creates more NOx. Same heat energy in less space means higher temperatures.

Verados create the same horsepower from 2.6L of displacement that requires 3.4L-4.2L from the other normally aspirated outboards. Same energy less space equals higher temps.

Air which is roughly 80% nitrogen and 20% oxygen in high enough temperatures will form NOx. This requires no fossil fuel, only air and heat! The hydrogen and carbon in fossil fuel normally bonds to oxygen forming H2O and CO2 but an engine run lean rather than stoichiometric will have oxygen left after burning the fuel allowing nitrogen to bond to it, again if the temps are high enough.

posted 02-10-2013 09:07 AM ET (US)            

To be certain combustion of all fuel in the combustion chamber took place, it seems like it would be useful to always have a surplus of air, that is, to always be running toward the lean side of the mixture. Some outboard engine manufacturers even describe their systems with terms like lean-burn.

posted 02-10-2013 12:36 PM ET (US)            

quote:

---

It has also been mentioned in the past that a combustion chamber operating with a lean fuel-air mixture will tend to become hotter. Please explain why a lean fuel-air mixture tends to create higher temperatures.

---

It's not that running excess oxygen causes hotter temperatures, per se. It's more that the absence of excess fuel deprives the motor of it's cooling "fluid" which is the fuel itself. Part of the combustion process is the release of heat. And the rate of heat released is proportional the rate at which fuel is combusted. That's why at idle and low load, it's OK to run an engine at stoich, because at those low loads fuel is being burned at a slow enough rate that the internal components can reject the heat at the same rate it's put to them. But as you increase the load and thus the rates at which fuel is burned, eventually, the internal parts are subjected to heat input at rates greater than the rate they can reject it. As a result, they get hotter and hotter. With no "cooling help" the weakest link eventually fails due to thermal fatigue and the engine is destroyed. The "cooling help" is extra fuel in the mixture. Supercharged motors are a worst case scenario, because they are small, relative to their capability to burn fuel and air, with less mass to absorb and reject heat in comparison to motors that achieve their power levels from having more massive reciprocating assemblies.

posted 02-11-2013 02:28 PM ET (US)         

The reasons as mentioned have to do with the lean charge imparting more heat into the cylinder walls because of less hydrocarbon mass to carry the heat out the exhaust and the tendency for the boundary layer of oil and fuel on the cylinder wall to burn or wash off using the excess oxygen. This boundary layer acts as a insulation layer between the hot combustion gasses and the metal of the cylinder, it's not just for lubrication.

What must be remembered is an internal combustion engine is a heat engine, as such the hotter it runs the more efficient it is at creating mechanical work from heat energy. This must be balanced with the ability of the engines materials to stay in solid form under such heat.

quote:

---

Is it fair to say that the heat rise that can occur with lean combustion could be handled if the components of the combustion chamber and the engine block were designed to have the capacity to absorb the heat and dissipate the heat without damage? Or, in other words, the heat rise is only a problem for engine designers that were depending on a rich fuel mixture to help cool the combustion chamber. Is that true?

---

Yes see diesels, they run very hot and lean most with forced induction. This is why they are heavy and require a large oil capacity, in order to withstand and dissipate the heat. This is also why they are very efficient and also why they generate large amounts of NOx, thus requiring aggressive catalytic systems.

This is also why you see modern 4-stroke outboards utilizing lean burning ratios more aggressively than DI 2-strokes. The extra stroke and wet sump allow the engine to withstand higher cylinder temps for longer periods as compared to a 2-strokes. This is the reason behind the E-TEC running lean only up through the 2000's while a Suzuki or Honda runs lean well up into the 4000's. This is also why E-TECs require special piston alloys from Nasa, to withstand the greater temps. Note this is also why Gen2 Verados have forged pistons. Evinrude could have gone with forged pistons as well, instead of the Nasa alloy they just cost more but could be more durable as well.

posted 02-11-2013 03:37 PM ET (US)            

HC----NOX---CO
06.65 03.9 084.9 Evinrude 250
05.36 07.6 200.9 Suzuki DF 200
10.68 03.8 259.0 Yamaha F225
04.90 15.0 109.2 Mercury Verado 300

I would not conclude that E-TEC and Verado are similar.

posted 02-12-2013 12:38 AM ET (US)         

What about the E-TEC 300?

HC----NOX---CO
25.6 03.9 251 Evinrude 300

The E-TEC 300 is actually worse than the Verado 300, but it's from running rich vs lean so its fuel economy is probably worse as well.

How about a Gen I Verado 250 (gen 2 are not in the data):

HC----NOX---CO
11.09 4 278 Verado 250

Gen 1's ran richer obviously but within 3 star carb of 16.1 HC+NOx total while the Gen 2 300 blows that by only 3 g/kw-hr vs the E-TEC 300 blowing it by over 13!

posted 02-12-2013 08:37 AM ET (US)            

Regarding where various engines come in to the rating scheme, let me suggest that we get a finer grain of rating. Instead of just unitary values, could we describe the emission compliance in a decimal? For example, the VERADO engine rated Two-Star would be described as 2.0-Star if it just meet the criteria for the rating of Two-Star. If it exceeded the minimal standard for Two-Star and was halfway to Three-Star level, then it would be a 2.5-Star. If it were on the cusp of meeting the Three-Star, then it would be a 2.9-Star.

posted 02-13-2013 08:38 AM ET (US)            

quote:

---

This is the reason behind the E-TEC running lean only up through the 2000's while a Suzuki or Honda runs lean well up into the 4000's.

---

In further thought about this topic, this comparative statement bothered me. I don't think this is accurate.

The "lean" mode up to 2000 RPM or so that you refer to in the E-TEC is the stratified charging mode. The Ficht and the Optimax also employ a stratified charging mode. In that mode, there is a rich blob of atomized fuel injected into the cylinder near the spark plug and that blob is surrounded by air. In this mode, the overall cylinder is run very lean. None of the 4-stroke outboard makers including Suzuki and Honda have DFI systems and thus cannot employ any stratified charging of the cylinders. So I think the comparison of the E-TEC and Suzuki or Honda is one of apples to oranges. They are just different.

While the 2-stroke fires the piston every time and the 4-stroke fires every other time, the amount of fuel combusted in each power stroke of the 2-stroke combustion chamber is approximately 1/2 that which is combusted in the chanber for each power stroke of the 4-stroke assuming the same number of cylinders. If we compare a V6 2-stroke 150 to a I4 4-stroke 150, for example, the fuel charge per cylinder is less than 1/2.

By the way, 4-stroke engines that use direct fuel injection (DFI), such as the engines that I have in two of my cars, employ stratified charging at low engine speeds/loads just like the E-TEC and the FICHT before that. DFI is becoming more mainstream in automobile engines. As it becomes more mainstream, maybe it will make its way to 4-stroke outboards someday.

posted 02-13-2013 11:52 AM ET (US)         

This is because it has a higher power density, which as you have mentioned multiple times in the past, they need less displacement to create the same power. Just as the Verado, same power less space equals higher temps. This is compounded by the lack of wet sump and the cylinders firing twice as often allowing less downtime between fires for the heat to be carried away from the cylinder walls and pistons by the conductive mass of the engine and the non existent crank case oil.

quote:

---

None of the 4-stroke outboard makers including Suzuki and Honda have DFI systems and thus cannot employ any stratified charging of the cylinders.

---

This is incorrect, most lean burn designs employ a form of stratified charging, even the old carburated ones! Modern EFI outboards from Suzuki and Honda use precise injector control along with very specific intake dynamics to achieve a non-homogeneous charge. Honda's automobiles have been doing lean stratified charges since the 70's using CVCC.

posted 02-15-2013 01:56 PM ET (US)            

I would like to see a representation of the CARB star ratings expressed with more granularity. Presently we only get CARB rating to the whole digit, always rounding down, I presume. I would like to see a few ratings expressed as decimal CARB ratings. By that I mean as follows: if the level of some air pollution to meet the Two-Star rating were said to be 200, and if the level of the Three-Star rating were said to be 300, I would like to see a rating that showed the relative air pollution of the engine. For example, if a particular engine rated 250 on my scale, it would only get a Two-Star. I would call it a 2.5-Star. If an engine just reached a rating on my scale of 300, it would be Three-Star. If an engine were actually rated 350, I would call it a 3.5-Star. With this in mind, could someone tell me the decimal-Star rating of

--the E-TEC 150
--the E-TEC 300
--the VERADO 150
--the VERADO 300

posted 02-16-2013 12:09 AM ET (US)         

It is just HTML/javascript so it should work for everyone with a modern browser:

http://jsfiddle.net/PWGnh/n/

Note if you make changes everyone will see them, so if you wish to experiment use the Fork button. It should be easy to add your own data.

I am not entirely sure about the average power rating for the engine "family", they mention sales weighted average, mine limits are slightly lower than the ones listed on the spreadsheets, so I would imagine the average powers are actually lower than what I am deriving.

posted 02-16-2013 11:28 AM ET (US)         

I noticed jsFiddle seems to be running slow, it seems they they are suffering from their own popularity and the server are very overloaded. It is a popular tool in programming circles for quickly sharing ideas. There is a similar service at jsBin.com that I may make a copy of there if this continues.

The basic premise of the decimal star is normalizing the HC+NOx value to a percentage of the total HC+NOx range in a star. The core piece of code that does that is:

engineData.star = engineData.starLimit.star +((engineData.starLimit.max-engineData.hcNox)/engineData.starLimit.range);

posted 02-17-2013 10:01 AM ET (US)            

The Suzuki engines were impressive.

I wonder how the 150 HP Gen2 Verado fares. It's now the baby of the family. My engine is the 135 HP Gen2 Verado but because it is no longer produced the numbers are pretty meaningless unless one is planning to install a new higher HP ECU.

posted 02-17-2013 10:31 AM ET (US)            

It appears that many engines rated Three-Star are well above the 3.0-decimal Star level. Manufacturers selling those engines are accumulating a lot of emission credits which they could use to create room in their sales mix for non-compliant engines, that is, engines rated below 3.0-decimal stars.

For a manufacturer selling mainly Three-Star engines with only one or two models rated Two-Star, there must be a wealth of emission credits available to provide the offset to the Two-Star engines. For a manufacturer hoping to sell a large number of Two-Star engines, there must be a more careful balance in the product mix.

posted 02-17-2013 12:16 PM ET (US)         

It is very easy to add new data, it is in JSON format, and stored at the top of the source code in the engineData variable: http://en.wikipedia.org/wiki/JSON

It is structured as an array of engine family objects with each family containing an array of engine data objects. Emissions can be input as hc and nox separately or as hcNox combined for data coming from the supplemental EPA spreadsheets where it is not reported broken down.

All data comes from here: http://www.epa.gov/otaq/certdata.htm#marinesi

posted 02-18-2013 10:51 AM ET (US)            

jharrell,

posted 02-18-2013 10:56 AM ET (US)            

If the EPA continues to tighten their emission standards (decrease the amount of allowable emissions) how close are we to needing bolt on devices such as catalytic converters ?

posted 02-18-2013 11:29 AM ET (US)         

quote:

---

The 4-stroke Merc 150 is family CM9XM03.02GB and may be listed as having 2.999L displacement

---

In that case just the last entry labeled "150 3L GB" is the new engine, it was listed as exactly 3L like the rest.

I have updated to a new version removing the other entries and relabeling:

posted 02-18-2013 11:36 AM ET (US)         

quote:

---

If the EPA continues to tighten their emission standards (decrease the amount of allowable emissions) how close are we to needing bolt on devices such as catalytic converters ?

---

In my opinion it's inevitable, just look at the difference in emissions on the Mercury stern drives with cats in the data, we are talking 1/10th the emissions of a 3 star OB. Not only that now the engines can be run leaner and hotter while staying easily within the emission standards making them more fuel efficient and more powerful.

posted 02-18-2013 12:07 PM ET (US)            

For example:

--on the E-TEC V6 family the values are: 5, 16.1, 36, 45

--on the Yamaha Mid range the values are: 5, 17.1, 38.2, 47.7

posted 02-18-2013 12:18 PM ET (US)         

The actual description is "Where P means the average power in kW (sales-weighted) of the subject engine family". http://www.arb.ca.gov/msprog/macs/mac0301/mac0301.pdf

Unfortunately I don't know the sales weighting or what exact models are in each family so I guessed grouping engines by displacement and cycle and it seems to agree with the EPA data. They have a column in the supplemental spreadsheet which denotes the limit for the particular engine.

posted 02-18-2013 03:18 PM ET (US)            

I had a Corvette that I got into tuning. I was surprise to find GM had put in the ECM source code a highway lean burn operation. I was able to enable it and easily pick up another 3-MPG highway, about 10-percent increase, by just turning it on. It ran about 15.2:1 [air-fuel-ratio] and a duty cycle of 30-seconds-on, 30-seconds-off. Other tuners were able to get 5-MPG [increase] by tweaking it further.

posted 02-28-2013 05:06 PM ET (US)            

Honda has lean burn combustion chamber. The automobile engines with Honda lean burn combustion chambers that are for sale in [California] run stoichiometric air-fuel ratio like most automobile engines.

posted 03-02-2013 09:32 AM ET (US)            

There seems to be a trend in the combustion process which causes a rise in NOx emissions in the combustion chamber under lean fuel-air mixtures. The lean fuel-air mixtures are used to enhance fuel economy. In order to maintain compliance with exhaust emission and use lean fuel-air mixtures, it appears to me that the trend is to treat the exhaust gases outside of the combustion chamber in a catalytic convertor. The higher NOx content in the exhaust gas can be changed in the catalytic convertor.

Whether or not marine outboard engines are adaptable to this technique seems to be a consideration undertaken by CARB, as evidenced by the studies done by Mercury regarding use of a catalytic convertor on their VERADO engines.

It seems like there is a natural, physical, chemical barrier in place for the combustion chamber, lean fuel-air mixtures, and NOx emissions. The regulatory agencies must be cognizant of this limitation. In order to move beyond this limit, it seems inevitable that the higher NOx emission has to be handled downstream of the combustion chamber. This seems to imply that if manufacturers of marine outboard engines want to meet exhaust emission regulations and improve the fuel economy of their engines, they will have to develop methods for handling the higher NOx exhaust downstream of the combustion chamber.

posted 12-14-2013 01:26 PM ET (US)            

Notice of the previously proposed and now 2010 emissions standards can be seen here www.epa.gov/nonroad/marinesi-equipld/420f07032.pdf . I cannot find any newer proposed standards that have not been enacted. One interesting thing to note from the proposed to the actual emissions standards (the 2010 standards) is that the proposed standards set CO emissions at 200 g/kw-hr for 40kW and above. The enacted standard is 300. It's not clear to me whether that was a typo or it was subsequently revised higher to the current 300 g/kw-hr standard.

However, what is clear from the comments (see cfpub.epa.gov/si/si_public_file_download.cfm?p_download_id=499576 ) is that the CO standard was purposely set so that outboards would NOT have to use catalytic converters because the technology as used in outboard motors is far more difficult to implement than in the case of stern drives and inboards and is unproven. I recall back in 2007 that some of the 4-stroke outboards had CO emissions that were higher than 200 g/kw-hr but few if any had emissions higher than 300 g/kw-hr. I don't recall any of the DFI 2-stroke outboards having CO emissions above 200 and some were below 100. So to the extent that the 200 g/kw-hr in the proposed regulations was accurate, it's likely that there was some industry push back from the 4-stroke makers.